

A187758


Number of ways to write n=x+y (x,y>0) with 2x3, 2x+3, 6y+1 and 6y+5 all prime


2



0, 0, 0, 0, 1, 2, 2, 2, 2, 3, 4, 2, 2, 3, 3, 3, 2, 3, 3, 4, 5, 3, 6, 5, 4, 6, 3, 5, 4, 3, 6, 2, 4, 5, 5, 4, 4, 6, 5, 4, 6, 5, 4, 5, 7, 5, 2, 3, 6, 4, 5, 4, 5, 7, 6, 9, 5, 4, 9, 5, 4, 5, 5, 4, 5, 6, 3, 8, 5, 8, 8, 3, 7, 5, 3, 5, 3, 5, 4, 9, 6, 4, 9, 7, 5, 8, 7, 8, 6, 9, 8, 2, 7, 7, 5, 6, 2, 10, 6, 3
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OFFSET

1,6


COMMENTS

Conjecture: a(n)>0 for all n>4.
This has been verified for n up to 10^8. It implies that there are infinitely many cousin primes and also infinitely many sexy primes.


LINKS

ZhiWei Sun, Table of n, a(n) for n = 1..20000
ZhiWei Sun, Conjectures involving primes and quadratic forms, arXiv:1211.1588.


EXAMPLE

a(5)=1 since 5=4+1 with 2*43, 2*4+3, 6*1+1 and 6*1+5 all prime.


MATHEMATICA

a[n_]:=a[n]=Sum[If[PrimeQ[2k3]==True&&PrimeQ[2k+3]==True&&PrimeQ[6(nk)+1]==True&&PrimeQ[6(nk)+5]==True, 1, 0], {k, 1, n1}]
Do[Print[n, " ", a[n]], {n, 1, 100}]


CROSSREFS

Cf. A023200, A046132, A023201, A002375, A187757, A199920, A219055, A218867, A220455.
Sequence in context: A219795 A082602 A216644 * A171931 A221530 A262944
Adjacent sequences: A187755 A187756 A187757 * A187759 A187760 A187761


KEYWORD

nonn


AUTHOR

ZhiWei Sun, Jan 03 2013


STATUS

approved



